As is known per se, such a variable speed drive comprises a driving and a driven pulley with parallel axes, and an endless belt looped over the pulleys. Each of the pulleys generally comprises two coaxial pulley halves facing each other and fixed for rotation with a rotatable shaft. One of the pulley halves referred to as the fixed pulley half is, in operation, axially fixed to the rotatable shaft and the other pulley half, known as the movable pulley half, is mounted for axially movement with respect to the fixed half, at least part of a side of at least one of the pulley halves is frustoconical. Resilient return means bear axially against an annular abutment member fixed for rotation with the rotatable shaft and axially fixed with respect thereto, urging the movable pulley half in the direction of the fixed pulley half.
The present invention relates more particularly though not exclusively to the case in which the resilient return means associated with the movable pulley half of one such pulley comprise a diaphragm spring having a Belleville washer peripheral portion which bears axially against the movable pulley half and a central portion divided into radial fingers which bears axially against the associated abutment member.
One of the problems posed in the construction of variable speed drive pulleys of this type is to limit, insofar as possible, the wear produced in contact between the diaphragm spring and the abutment.
It has been found that in service the movable pulley half of such a pulley is subjected to an eccentric movement around the rotatable shaft by reason of the action of the belt thereon being exerted only along a fraction of the circumference and this eccentric movement is transmitted by the diaphragm spring to the movable member. This is, of course, a movement of small magnitude but which, being repeated each revolution of the pulley, is gradually the cause of the pronounced wear of the diaphragm spring fingers in contact with the abutment member against which they bear, the hardness of the fingers generally being less than that of the abutment member.